Gel electrophoresis is commonly used to separate and analyze biological substances such as proteins and nucleic acids. In gel electrophoresis, a polyacrylamide or agarose gel in a tube or sandwiched as a slab between glass or plastic plates is placed in an apparatus in which an electric potential is applied to the gel, causing the biological substances to travel through the gel. As the substances travel through the gel, they separate from each other based on size, charge density, and/or conformation to form bands.
After electrophoresis, the cassette plates are typically removed prior to staining and/or visualizing pre-labeled bands in the gel with an ultraviolet-activated or excited dye because the plate material can block ultraviolet light.